Amyloid β (Aβ) precursor protein (APP) is a 100-140 kDa transmembrane glycoprotein that exists as several isoforms (1). The amino acid sequence of APP contains an amyloid domain, which can be processed and released by two-step proteolytic cleavage (1). The extracellular deposition and accumulation of the released Aβ fragments form the main components of amyloid plaques in Alzheimer's disease (1). Several fragments corresponding to progressive APP processing at alternative cleavage sites have been identified (2). These include Aβ (1-37), Aβ (1-39), Aβ (1-40), and Aβ (1-42) (2). These fragments can also be N-terminally modified to generate pyroglutamate-3 Aβ (pE3-peptide) (3). Fragment-specific and pan-Aβ antibodies are used to detect and examine relative levels of individual Aβ fragments.